The evolution of species on the land is linked to and driven
by various climatological and geological changes that operated
on the land surface of the earth.
As we will discuss later, the earth currently has significant
climate variations on a timescale of 100,000 years. In addition,
over the last 200-250 million years the earth is experiencing
an era go global tectonic motion which makes
the land surface a Dangerous Place to Live:
means that the crust of the earth is divided into
large connected units, all of which are moving relative to one
another and colliding with one another in various ways.
The idea of Plate Tectonics was first published by the German
Alfred Wegener in 1915 but this theory was largely ridiculed
until magnetic mapping of the ocean floor was done in the late 50's.
This history of the acceptance of this theory is summarized
Summary of Evidence for Plate Tectonics:
Now it is recognized that the surface of the earth can be divided up
into roughly 10--12 large scale plates
and perhaps a number of smaller ones as in the case of the
- The continents appear that they could fit together like
a Jigsaw Puzzle. Just a coincidence?
- Similar fossil records are found in Brazil and North Africa -->
could just mean that the climates and hence vegetation and animal
life were similar
- Similar rock types are seen in Brazil and North Africa --> this
is much harder to explain away especially if the ages of the rock
types are similar.
- Sea Floor
Spreading --> Magnetic mapping of the ocean floor revealed
a history of polarity reversals that formed a mirror image about
the Mid-Atlantic Ridge. This indicates that the floor of the Atlantic
Ocean is created at the mid Atlantic ridge due to crustal separation.
As magma issues forth and solidifies, it records the orientation of
the earth's magnetic field at the time of solidification. These
newly formed rocks are then carried either East or West of the
Mid-Ocean ridge. The floor of the Atlantic Ocean is thus an Age
sequence with newly formed rock appearing at the Mid Atlantic Ridge and
the oldest rocks being at the North American and European Coastlines.
The time of transport from the mid Atlantic ridge to these coastlines
is about 210 million years which indicates a total sea floor motion of
about 1.5 inches per year.
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